A plume of hexavalent chromium, a metal used in industrial production that the Centres for Disease Control and Prevention calls a "well-established carcinogen,'' has spread under Garfield, New Jersey, putting about one-tenth of the city's homes - about 600 structures and 3600 residents - at risk.

The Environmental Protection Agency is about to start drilling on the spill site to determine how much chromium is pooled beneath and remove tainted soil. The agency is also testing the broader area to determine how it will be cleaned up. Now a group of scientists from New York University is working to assess how much chromium residents may have been exposed to.

Researchers will collect toenail clippings from city residents. The nails will be tested for traces of chromium. Because toenails grow slowly, it is possible to see how much chromium has accumulated in the body over the past 18 months or so, said Judith Zelikoff, a professor of environmental medicine at New York University.

"Our major goal is to try to relieve their fears,'' Professor Zelikoff said. "With the economy, they can't sell their homes. They don't know if they got exposed.''

The contamination started 30 years ago, when thousands of pounds of hexavalent chromium - the same stuff that sickened Californians whose story was told in the film Erin Brockovich - leaked from a tank at the EC Electroplating Co., a factory surrounded on all sides by houses and apartments.

The state started cleaning up the spill but stopped two years later. In 1993, chromium was found at a now-shuttered firehouse and later in homes.

The EPA designated the area as a Superfund site - marking it as of the nation's most toxic uncontrolled hazardous waste sites - in 2011, and officials cautioned residents to stay out of their basements to prevent potential chromium exposure.

EPA officials removed chromium from the building and demolished it last year, and found that some tanks had holes in them, potentially releasing even more chromium into the groundwater.

Officials say the contamination has not affected the city's drinking water, which is drawn from an outside source. Instead, they worry that people could inhale chromium dust that has been found in basements where groundwater has leached in.

The chromium plume is about 1.2km wide and slightly more than 200m long, EPA officials said. The substance has travelled from the site underneath the Passaic River and into the city of Passaic. The agency has installed about 40 monitoring wells to monitor how far the metal has spread.

"We're trying to find out the extent of the plume,'' said Rich Puvogel, a project manager with the EPA.

High quantities of the metal have been found in 14 homes that have since been cleaned up. Trace amounts were found in 30 to 40 homes. Testing continues, and a nearby school did not show elevated chromium levels.

Cathy Garrone, who bought a house in the neighborhood in 1985, walked her small dog recently across the street from the site where the plant once stood, a lot now fenced off and peppered with mounds of rocks and dirt.

She said she wouldn't have bought there if she had known about the chromium spill, and thinks much more testing needs to be conducted, both of the environment and people.

"I'd like them to do more testing to assure my safety,'' she said.

The research study is being done in conjunction with the city of Garfield. Officials are hoping the testing can bring some answers to residents.

"It's just been left,'' Professor Zelikoff said. "A lot of people made mistakes.''

Professor Zelikoff and her team hope to test as many as 250 residents; some must live close to the plume and others about 5 kilometres away as a control group. When residents sign up, they will be given a kit that contains stainless steel toenail clippers (cheap ones contain chrome), instructions on how to clip the nails (samples from all 10 are needed) and an envelope for the clippings.

It will take weeks to know the results, and people will be advised by public health nurses and others once the results return.

Test subjects must be between 18 and 65, have lived in Garfield for at least two years, not take chromium supplements, and not smoke.

Many residents are immigrants and relative newcomers, and some do not know about the contamination, Professor Zelikoff said. City officials are working to educate residents, disseminating information about the cleanup to local churches and in four languages: English, Spanish, Polish and Macedonian, said city manager Tom Dutch.

Mr Dutch said an initial health consultation indicates that there's no higher incidence of cancer in the neighbourhood than anywhere else in the city, but he thinks the issue needs additional scientific testing.

"I have some concerns,'' Dutch said. "There are residents who have come to meetings and said, 'This one died, that one died,' and I think it warrants further investigation.''

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